Fix safe_yaml depercation message

There is a depercation message "The method 'YAML.enable_arbitrary_object_deserialization!'
is deprecated and will be removed in the next release of SafeYAML -- set
the SafeYAML::OPTIONS[:default_mode] to either :safe or :unsafe.", this
commit fixes it.
Merge pull request #1529 from kavu/fix_safe_yaml_depercation_message

Fix safe_yaml depercation message
add decimal and float range query

extending @akm integer range query code to float
and decimal fields
Merge pull request #1530 from thiagobrandam/decimal_and_float_comparison

Add decimal and float range query
Revert "use safe_send instead of send for association's value"

This reverts commit c1dd985b34d5159cfd2b636d0f726e938441c49b.
Ckeditor fix

See https://github.com/sferik/rails_admin/commit/e97f4fadff17b77e65c452be3ac4314adeb16748#commitcomment-2645547
Ckeditor [ci skip]

Remove old instances if found
fix the build
Add remove button for nested one form
Merge pull request #1534 from gokure/nested-one

Add remove button for nested one form
Fixed `ambiguous column name: updated_at` error in dashboard.
Merge pull request #1535 from softpro/master

Dashboard throws `ambiguous column name: updated_at`
Merge branch 'master' of https://github.com/sferik/rails_admin